T'Kahr was a Vulcan honorific, normally used for a learned person, which roughly translated to "teacher." (TOS novel: Dwellers in the Crucible) When one is referred to as a t'kahr, they are traditionally required to answer questions given to them. (TOS novel: The IDIC Epidemic) Some t'kahr, such as Spock, do not accept the role when dealing with those who don't wish to learn. (TOS novel: Dwellers in the Crucible) Presumably, it is separate from the title of T'Kehr. However, it could be an alternate spelling.